Tilt top anvil for a surgical fastener device

ABSTRACT

A tilt top anvil assembly is provided for use with a surgical stapling device for performing end-to-end anastomosis of tissue. The tilt top anvil assembly included an anvil head, a center rod and a biasing member. The anvil head is pivotally secured to the center rod about a transverse axis which is offset from the longitudinal axis of the center rod. The biasing member is supported on the anvil assembly at a position to urge the anvil head to a tilted reduced profile position. The anvil assembly includes a first abutment surface which is operatively connected to the anvil head is movable into engagement with a second abutment surface formed on a surgical stapling device during approximation of the anvil assembly to move the anvil head from the tilted reduced profile position to an operative firing position. When the anvil assembly is moved to the unapproximated or spaced position, the biasing member is positioned to return the anvil assembly back to its tilted reduced profile position.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/491,253, filed Mar. 30, 2004 which claims priority from PCTapplication Serial No. PCT/US02/32033, filed Oct. 4, 2002 which claimspriority from U.S. provisional application Ser. No. 60/327,727, filedOct. 5, 2001 all of which are incorporated herein by reference in theirentirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an anvil assembly for use with asurgical stapling device. More particularly, the present disclosurerelates to an anvil assembly having a normally tilted anvil head whichis usable with an open or a minimally invasive surgical staplinginstrument for performing circular anastomosis of hollow tissue organs.

2. Background of Related Art

Anastomosis is the surgical joining of separate hollow organ sections toallow the sections intercommunicate with each other. Typically, ananastomosis procedure follows surgery in which a diseased or defectivesection of hollow tissue is removed and the remaining end sections areto be joined. Depending on the desired anastomosis procedure, the endsections may be joined by either circular, end-to-end, end-to-side orside-to-side organ reconstruction methods.

In a circular anastomosis procedure, the two ends of the organ sectionsare joined by means of a stapling instrument which drives a circulararray of staples through the organ end sections and simultaneously coresand removes any overlapping tissue to free a tubular passage. In someapplications of a circular anastomosis procedure, on anvil rod having anattached anvil head is mounted to the distal end of a surgical staplinginstrument shaft prior to insertion of the instrument into the tissue tobe anastomosed. However, in other applications, it is preferable toutilize a detachable anvil rod which may be mounted to the instrumentsubsequent to positioning of the instrument and the anvil assemblywithin respective tissue sections. In such instances, the staplinginstrument and the anvil assembly are separately delivered to theoperative site. Each tissue section is then secured to a respectiveanvil or staple holding component by a purse string suture. The anvilassembly is mounted to the surgical instrument by inserting a mountingportion of the anvil rod within the distal end of the instrument so thata mounting mechanism within the instrument securely engages the rod.Preparation of the tissue sections to be joined and mounting of theanvil rod to the instrument are performed, preferably, using minimallyinvasive surgical techniques, i.e., under laparoscopic guidance.

A particular difficulty concerning the aforedescribed approach toperform anastomosis of hollow body organs with a detachable anvilassembly, whether the anastomosis is performed laparoscopically or byother conventional open surgical techniques, concerns delivery andplacement of the anvil assembly at the desired location within thehollow organ. This difficulty is attributed to, inter alia, the factthat the anvil assembly, particularly, the rigid, immovable anvil head,presents an obtrusive profile which engages the inner wall of the holloworgan during advancement therethrough. In some instances, the dimensionof the anvil head is greater than the cross-sectional dimension of thehollow organ through which it must pass. Consequently, advancement ofthe anvil assembly through the hollow organ can be traumatic and isimpeded and possibly prevented. Furthermore, if a surgical procedure isbeing performed laparoscopically, difficulty with maneuvering the anvilassembly through the hollow organ may require abandonment of suchlaparoscopic approach and necessitate conversion to a conventional openlaparotomy to complete the anastomosis.

In order to reduce the transverse profile of the anvil assembly duringplacement and removal of the anvil assembly from a hollow organ, anvilassemblies having a tiltable anvil head have been developed. One suchanvil assembly is described in U.S. Pat. No. 6,053,390, filed on May 10,1999, which is incorporated herein by reference in its entirety. Thepivotable anvil head is normally locked in the operative firingposition. Upon firing the stapling device, the lock is released and theanvil head is forced to the tilted position by a spring.

Despite recent improvements to circular anastomosis instruments, a needstill exists for an improved anvil assembly usable with a circularanastomosis instrument which includes an anvil head that is easier todeliver into hollow tissues to be joined, that can be delivered withless contact with such tissues, and also that automatically pivotsbetween tilted and operative positions during delivery and removal ofthe instrument from the tissues.

SUMMARY

In accordance with the present disclosure, a tilt top anvil assembly isprovided for use with a surgical stapling device for performingend-to-end anastomosis of tissue. The tilt top anvil assembly includesan anvil head, a center rod and a biasing member. The anvil head ispivotally secured to the center rod about a transverse axis which isoffset from the longitudinal axis of the center rod. The biasing memberis supported on the anvil assembly at a position to urge the anvil headto a tilted reduced profile position. The anvil assembly includes afirst abutment surface which is operatively connected to the anvil headand is movable into engagement with a second abutment surface formed ona surgical stapling device during approximation of the anvil assembly tomove the anvil head from the tilted reduced profile position to anoperative firing position.

In one preferred embodiment, the center rod includes a longitudinalbore. An outer sleeve is slidably positioned within the longitudinalbore and an inner sleeve is slidably positioned within the outer sleeve.The inner and outer sleeves are pivotally connected to the anvil head byrespective links. The biasing member is positioned within thelongitudinal bore to urge the inner sleeve towards the anvil head tourge the anvil head to the tilted reduced profile position. The outersleeve includes a first abutment member which is positioned to engage asecond abutment surface supported on a surgical stapling device when theanvil assembly is moved from a position spaced from a shell assembly ofthe surgical stapling device to an approximated position in closealignment with the shell assembly of the surgical stapling device. Uponengagement between the first and second abutment surfaces and continuedapproximation, the anvil head is pivoted from the tilted reduced profileposition to the operative firing position. When the anvil assembly ismoved back to the spaced position, the biasing member urges the anvilhead back to the tilted reduced profile position. Thus, the anvil headis automatically moved to a tilted reduced profile position duringdelivery and removal of the instrument from the anastomatic site.Alternatively, other linkage mechanisms for pivoting the anvil head fromthe tilted reduced profile position to the operative firing position areenvisioned.

In another preferred embodiment, a shell assembly of the surgicalstapling device may include an annular sleeve positioned therein.Preferably, the second abutment surface is formed on the annular sleeveat a position to engage the first abutment surface on the anvilassembly. Alternately, the second abutment may be positioned at otherlocations on the surgical stapling device.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the presently disclosed tilt top anvil assemblyare described hereinbelow with reference to the drawings wherein:

FIG. 1 is a side view of one preferred embodiment of the presentlydisclosed tilt top anvil assembly with the anvil head in the tiltedreduced profile position;

FIG. 1A is a bottom partial cross-sectional view of the anvil assemblyshown in FIG. 1;

FIG. 2 is a side cross-sectional view of the tilt top anvil assemblyshown in FIG. 1 with the anvil head in the tilted reduced profileposition;

FIG. 3 is a side cross-sectional view of the tilt top anvil assemblyshown in FIG. 1 with the anvil head positioned between the tiltedreduced profile position and the operative firing position;

FIG. 4 is a side cross-sectional view of the tile top anvil assemblyshown in FIG. 1 with the anvil head in the operative firing position;

FIG. 5 is a side cross-sectional view of the tilt top anvil assemblyshown in FIG. 1 with the anvil head positioned in the tilted reducedprofile position and secured to the shell assembly of a surgicalstapling device;

FIG. 6 is a side cross-sectional view of the tilt top anvil assemblyshown in FIG. 1 with the anvil head positioned between the tiltedreduced profile position and the operative firing position;

FIG. 7 is a side cross-sectional view of the tilt top anvil assemblyshown in FIG. 1 with the anvil head positioned in the operative firingposition;

FIG. 8 is a side view of the tilt top anvil assembly shown in FIG. 1with the anvil head positioned in the operative firing position andsecured to the shell assembly of a surgical stapling device;

FIG. 9 is a top perspective view of the annular sleeve of the shellassembly of a surgical stapling device with which the presentlydisclosed tilt top anvil may be used;

FIG. 10 is a side cross-sectional view of the body of the shell assemblyshown in FIG. 8;

FIG. 11 is a top view of the body of the shell assembly shown in FIG.10;

FIG. 12 is a side cross-sectional view of another preferred embodimentof the presently disclosed tilt top anvil assembly secured to the shellassembly of a surgical stapling device with the anvil head positioned inthe operative firing position;

FIG. 13 is a side cross-sectional view of the tilt top anvil assemblyshown in FIG. 12 with the anvil head in the tilted reduced profileposition;

FIG. 14 is a side perspective view of the tip top anvil assembly shownin FIG. 12 with the anvil head positioned in the tilted reduced profileposition and a removable trocar engaged with the center rod; and

FIG. 15 is a side perspective view from a different side of the tilt topanvil assembly shown in FIG. 14 with the removable trocar removed fromthe anvil center rod.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the presently disclosed tilt top anvil assemblywill now be described in detail with reference to the drawings in whichlike reference numerals designate identical or corresponding elements ineach of the several views.

Referring to FIGS. 1 and 2, anvil assembly 10 includes an anvil post 12,an anvil head 14, an anvil plate 16, a center rod 18, an inner sleeve 20and an outer sleeve 22. Anvil head 14 includes a centrally locatedthrough bore 24 dimensioned to receive anvil post 12, an inner annularrecess 26 and an outer annular recess 28. Outer annular recess 28 isconfigured to receive anvil plate 16. Anvil plate 16 includes a tab 30(FIG. 1A) which is dimensioned to be received within a slot 32 formed inanvil head 14. Tab 30 and slot 32 cooperate to position anvil plate 16in the proper orientation within outer recess 28. Inner annular recess26 is configured to receive a cutting ring 34 that includes a centralopening dimensioned to be positioned about anvil post 12 and a portionof anvil head 14 defining annular recess 26.

Anvil post 12 includes a transverse bore for receiving a pivot member38. Pivot member 38 pivotally connects anvil post 12 to one end ofcenter rod 18. Preferably, pivot member 38 includes a pin or post whichdefines a transverse axis which is spaced laterally from thelongitudinal “x” axis of center rod 18 such that anvil head 14 can pivotapproximately 90 degrees from an operative position (FIG. 4) in which aplane defined by the tissue contact surface of the anvil head 14 issubstantially perpendicular to the longitudinal axis of center rod 18 toa tilted reduced profile position (FIG. 2) in which anvil head 14 issubstantially parallel to the longitudinal axis of center rod 18.Alternately, other types of pivot members at a variety of locations inrelation to the axis “x” of the center rod may be incorporated into theanvil assembly.

Center rod 18 includes a throughbore 40 having a first end 42 and asecond end 44. Preferably first end 42 includes at least one bore 46dimensioned to receive a suture or the like to facilitate positioning ofanvil assembly 10 within a hollow organ. Second end 44 of throughbore 40is dimensioned to slidably receive inner sleeve 20 and outer sleeve 22.Outer sleeve 22 is slidably positioned within second end 44 ofthroughbore 40, and a portion of inner sleeve 20 is slidably positionedwithin outer sleeve 22. A spring or biasing member, e.g., coil spring41, is positioned in second end 44 of throughbore 40 abutting innersleeve 20 to urge inner sleeve 20 to an advanced position toward thedistal end of anvil assembly 10. A drive link 52 is pivotally connectedat one end to outer sleeve 22 and at the other end to anvil post 12. Areturn link 50 is pivotally connected at one end to inner sleeve 20 andat the other end to anvil post 12. Outer sleeve 22 includes an abutment54 (FIG. 4) which will be discussed in further detail below.

Center rod 18 is dimensioned to releasably engage an anvil retainer (notshown) of a circular anastomosis surgical stapling device. One suchsurgical stapling device having an anvil retainer and with which anvilassembly 10 may be used is disclosed in U.S. provisional patentapplication Ser. No. 60/281,259, filed Apr. 3, 2001, (“the '259application”) which is incorporated herein in its entirety by reference.Center rod 18 includes an annular projection 56 which is dimensioned tolockingly engage the anvil retainer. A guide collar 60 is monolithicallyformed with center rod 18. Alternately, guide collar 60 may include asleeve which is separately formed from center rod 18. Guide collar 60includes circumferentially spaced splines 62 which function to alignanvil assembly 10 with the shell assembly 100 (FIGS. 5-8) of thesurgical stapling device during movement of the anvil assembly from apositioned spaced from a shell assembly of the surgical stapling deviceto an approximated position in close alignment with the shell assembly.

Inner sleeve 20 is moveable between an advanced position and a retractedposition. The inner sleeve biasing member 41 normally urges inner sleeve20 to the advanced position. In the advanced position, return link 50 ismoved towards anvil head 14 to pivot anvil head 14 about pivot member 38to the tilted reduced profile position (FIG. 2).

Referring to FIGS. 5-8, anvil assembly 10 is moved to the operativeposition by advancing abutment 54 of outer sleeve 22 towards anvil head14. This will occur automatically when anvil assembly 10 is secured tothe anvil retainer of a surgical stapling device and the device isapproximated. More specifically, during approximation of a surgicalstapling device, abutment 54 is engaged by an abutment 70 positioned onor within the shell assembly 100 of a surgical stapling device toadvance outer sleeve 22 in the direction indicated by arrow “A” in FIGS.5 and 6 towards anvil head 14. Abutment 70 may be provided on an annularsleeve 80 adapted to be fitted within the shell assembly of a surgicalstapling device. Movement of outer sleeve 22 towards anvil head 14advances drive link 52 towards anvil head 14 against the bias of theinner sleeve biasing member 41 to pivot anvil head 14 in the directionindicated by arrow “B” in FIG. 6 from the tilted reduced profileposition (FIG. 5) to the operative firing position (FIG. 7). Thereafter,when the surgical stapling device is moved from the approximatedposition to the unapproximated or spaced position and abutment 54 ismoved distally out of engagement with abutment 70, inner sleeve biasingmember 41 will return anvil assembly 10 to its tilted reduced profileposition.

Referring to FIGS. 5-11, one preferred embodiment of annular sleeve 80including abutment 70 is illustrated. Annular sleeve 80 includes a firstcylindrical body portion 82 and a second cylindrical body portion 84.Second cylindrical body portion 84 has a diameter larger than that ofthe first cylindrical body portion 82 such that a shoulder 86 is definedon an internal wall of sleeve 80 between first and second portions 82and 84. Second body portion 84 includes four elongated cutouts 88 (FIG.9, only one is shown) and a window 90. Cutouts 88 are dimensioned to beslidably positioned over ribs 92 (FIG. 11) formed within shell assembly100. Sleeve 80 is formed of a material having some flexibility tofacilitate positioning of window 90 over a stop 94 (FIG. 10) formedwithin shell assembly 100, such that stop 94 is axially slidablyconfined within window 90. Alternately, sleeve 80 may be configureddifferently, i.e., sleeve 80 need not be annular but rather may includean abutment, fixed or movable, having any configuration positioned toengage the first abutment on the anvil assembly.

In use, second body portion 84 of annular sleeve 80 is positioned withinshell assembly 100 with second body portion 84 slidably positioned overinner cylindrical portion 102 of shell assembly 100 (FIGS. 5-7), cutouts88 positioned over ribs 92 (FIG. 11) and window 90 positioned over stop94. A spring biasing member, preferably a coil spring 96, is positionedbetween shoulder 86 of annular sleeve 80 and a cutout 104 formed oninner cylindrical portion 102 of shell assembly 100. Biasing member 96is positioned to urge annular sleeve 80 towards anvil head 14. Abutment70 is formed on the distal end of first cylindrical portion 82 ofannular sleeve 80.

As discussed above, when anvil assembly 10 is secured to a surgicalstapling device and the device is approximated, abutment 54 on outersleeve 22 will engage abutment 70 (FIGS. 5-7). When this occurs, sincebiasing member 96 has a greater compressive strength than biasing member41, outer sleeve 22 will be advanced towards anvil head 14 when theanvil assembly is approximated further to move anvil head 14 from thetilted reduced profile position (FIG. 5) to the operative firingposition (FIG. 7). When anvil head 14 has been pivoted to the operativeposition and outer sleeve 22 cannot be advanced any further towardsanvil head 14, further approximation of the anvil head 14 and shellassembly 100 will compress biasing member 96 and cause annular sleeve 80to retract into shell assembly 100 in a telescoping fashion about innercylindrical portion 102 of shell assembly 100.

FIGS. 12-15 illustrate another preferred embodiment of the presentlydisclosed tilt top anvil assembly shown generally as tilt top anvilassembly 200. Tilt top anvil assembly 200 is substantially the same astilt top anvil 10 and includes anvil post 212, anvil head 214, anvilplate 216, center rod 218, inner sleeve 220 and outer sleeve 222. Adrive link 252 is pivotally connected at one end to outer sleeve 222 andat the other end to anvil post 212. A return link 250 is pivotallyconnected at one end to inner sleeve 220 and at the other end to anvilpost 212. Outer sleeve 222 includes abutment 254. Center rod 218includes a plurality of resilient arms 215 which flex outwardly toreleasably engage an anvil retainer (not shown) of a surgical staplingdevice or a removable trocar 270 (FIG. 14).

Tilt top anvil assembly 200 differs from tilt top anvil assembly 10 in afew respects which will be described hereinbelow. As illustrated in FIG.13, tilt top anvil assembly 200 is configured to permit anvil head 214to pivot with respect to center rod 218 to define an angle Θ of about20° with respect to the longitudinal axis of the assembly. (Note: anvilhead 14 tilts to a position substantially parallel to the longitudinalaxis of tilt top anvil assembly 10). The degree of tilt of anvil head214 is controlled by varying the length of slot 260 in center rod 218through which abutment 254 is movably positioned. Angle Θ can beincreased by shortening the length of slot 260 and decreased byincreasing the length of slot 260. It is preferred that angle Θ is notless than about 20°. When angle E) is greater than about 20°, there isless tissue resistance to pivoting anvil head 214 to the operativeposition when the device is approximated. However, it is envisioned thatthere are surgical applications in which it would be desirable to havean angle Θ of less than 20°.

Center rod 214 includes a cutout 261 positioned adjacent splines 262.Cutout 261 provides an area on center rod 214 which can be easilygrasped by a surgeon using a grasping tool.

The above-described anvil assembly is particularly suited for use inminimally invasive gastric bypass procedures. Such a procedure isdescribed in PCT application Serial No. PCT/US01/07105, filed Mar. 5,2001, and U.S. Provisional patent application Ser. No. 60/187,121, filedMar. 6, 2000, both of which are incorporated herein in their entirety byreference. Alternately, the above described anvil assembly may be usedin other surgical procedures especially those in which a reduced profileanvil assembly is desirable.

It will be understood that various modifications may be made to theembodiments disclosed herein. For example, abutment 70 need not beformed on a telescoping annular sleeve but rather may be a non-annularabutment which is movably or fixedly supported within the shell assemblyof a surgical stapling device. Therefore, the above description shouldnot be construed as limiting, but merely as exemplifications ofpreferred embodiments. Those skilled in the art will envision othermodifications within the scope and spirit of the claims appended hereto.

1. (canceled)
 2. A tilt top anvil assembly comprising: an anvil head; acenter rod; and engagement structure positioned on the anvil assembly;wherein the anvil head is pivotally secured to the center rod and ispivotable between an operative firing position and a tilted reducedprofile position, and the engagement structure being movable to move theanvil head between the tilted reduced profile position and the operativefiring position.
 3. A tilt top anvil assembly according to claim 2,further including a biasing member positioned to urge the anvil head tothe tilted reduced profile position.
 4. A tilt top anvil assemblyaccording to claim 3, wherein the center rod includes a longitudinalthroughbore, the anvil assembly further including an inner sleeve and anouter sleeve, the outer sleeve being slidably positioned within thecenter rod throughbore and being operably connected to the anvil headand the inner sleeve being slidably positioned within the outer sleeveand being operably connected to the anvil head, wherein the biasingmember is positioned to urge the inner and outer sleeves to a positionto move the anvil head to the tilted reduced profile position.
 5. A tilttop anvil assembly according to claim 4, further including a drive linkpivotally connected between the outer sleeve and the anvil head and areturn link pivotally connected between the anvil head and the innersleeve.
 6. A tilt top anvil assembly according to claim 5, wherein theengagement structure is positioned on the outer sleeve, the engagementstructure being positioned to engage a portion of a surgical staplingdevice during approximation of the anvil assembly to move the anvilassembly from the tilted reduced profile to the operative firingposition.
 7. A tilt top anvil assembly according to claim 2, wherein theanvil head is pivotally secured to the center rod by a pivot member, thepivot member having a transverse axis which is offset from thelongitudinal axis of the center rod.
 8. A tilt top anvil assemblyaccording to claim 2, wherein the engagement structure includes anabutment member.
 9. A tilt top anvil assembly according to claim 2,wherein the anvil head includes a cutting ring positioned to engage aknife provided on a surgical stapling device.
 10. A tilt top anvilassembly according to claim 2, wherein the center rod includes at leastone through bore dimensioned to receive a suture.
 11. A tilt top anvilassembly according to claim 2, wherein in the tilted reduced profileposition, an angle Θ defined between the longitudinal axis of the anvilassembly and a plane defined by a tissue contact surface of the anvilhead is not less than about 20°.
 12. A surgical stapling devicecomprising: a handle portion; an endoscopic body portion extendingdistally from the handle portion; a shell assembly supported on thedistal end of the endoscopic portion, the shell assembly housing aplurality of surgical fasteners; and a tilt top anvil assemblyconfigured to be positioned adjacent the shell assembly, the tilt topanvil assembly including an anvil head, and a center rod, the anvil headbeing pivotally secured to the center rod and being pivotable between anoperative firing position and a tilted reduced profile position, theanvil assembly including engagement structure positioned to move theanvil head from the tilted reduced profile position to the operativefiring position in response to approximation of the anvil assembly andthe shell assembly.
 13. A surgical stapling device according to claim12, wherein the anvil assembly includes a biasing member which ispositioned to urge the anvil head to the tilted reduced profileposition.
 14. A surgical stapling device according to claim 13, whereinthe center rod includes a longitudinal throughbore, the anvil assemblyfurther including an inner sleeve and an outer sleeve, the outer sleevebeing slidably positioned within the center rod throughbore and beingoperably connected to the anvil head and the inner sleeve being slidablypositioned within the outer sleeve and being operably connected to theanvil head, wherein the biasing member is positioned to urge the innerand outer sleeves to a position to move the anvil head to the tiltedreduced profile position.
 15. A surgical stapling device according toclaim 14, further including a drive link pivotally connected between theouter sleeve and the anvil head and a return link pivotally connectedbetween the anvil head and the inner sleeve.
 16. A surgical staplingdevice according to claim 15, wherein the abutment is positioned on theouter sleeve, the engagement structure being positioned to interact witha portion of the surgical stapling device during approximation of theanvil assembly to move the anvil assembly from the tilted reducedprofile position to the operative firing position.
 17. A surgicalstapling device according to claim 13, wherein the anvil head ispivotally secured to the center rod by a pivot member, the pivot memberhaving a transverse axis which is offset from the longitudinal axis ofthe center rod.
 18. A surgical stapling device according to claim 13,wherein engagement structure includes an abutment member.
 19. A surgicalstapling device according to claim 13, wherein the anvil head includes acutting ring positioned to engage a knife provided on the surgicalstapling device.
 20. A surgical stapling device according to claim 13,wherein the center rod includes at least one through bore dimensioned toreceive a suture.
 21. A surgical stapling device according to claim 13,wherein the engagement structure includes a first engagement membersupported on the tilt top anvil assembly and a second engagement membersupported adjacent the shell assembly, the first engagement member beingoperably connected to the anvil head and being movable during movementof the anvil assembly from a position spaced from the shell assembly toan approximated position into engagement with the second engagementmember to move the anvil head from the tilted reduced profile positionto the operative firing position.
 22. A surgical stapling deviceaccording to claim 21, further including an annular sleeve supportedwithin the shell assembly, the second engagement member being formed onthe annular sleeve.
 23. A surgical stapling device according to claim22, wherein the annular sleeve is movable from an extended position to aretracted position, a second biasing member being positioned to urge theannular sleeve to the extended position.
 24. A surgical stapling deviceaccording to claim 23, wherein the second biasing member has a greatercompressive strength than the first biasing member such that duringmovement of the anvil assembly from the spaced to the approximatedposition, when the first engagement member engages the second engagementmember, the anvil head is moved from the tilted reduced profile positionto the operative firing position prior to movement of the annular sleevefrom the extended position to the retracted position.
 25. A tilt topanvil assembly according to claim 12, wherein in the tilted reducedprofile position, an angle Θ defined between the longitudinal axis ofthe anvil assembly and a plane defined by a tissue contact surface ofthe anvil head is not less than about 20°.
 26. An anvil assemblycomprising: a center rod; and an anvil head pivotally secured to thecenter rod, the anvil head being adapted for pivotal movement from atilted reduced profile position to an operative firing position inresponse to movement of the anvil assembly in relation to a shellassembly of a surgical stapling device.